In spin-based systems, a spin-polarized current is used to set magnetization states of magnetoresistive devices. For example, through the spin-transfer torque (STT) effect, spin of electrons in a spin-polarized current can apply torque to a magnetic moment of a free layer in a magnetoresistive device (e.g. a magnetic tunneling junction (MTJ), a giant magnetoresistive (GMR) device). Electrons are spin polarized by the fixed layer of the magnetoresistive device. Depending on the electron flow direction and relative orientation of spin of electrons and the magnetization of the free layer, magnetization of the free layer can be set to be parallel or anti-parallel to the magnetization of the fixed layer.
One way to generate the spin-polarized current for setting magnetization states of magnetoresistive devices is through spin pumping. In spin pumping, a device injects a spin-polarized current into a spin channel, and the spin-polarized current drifts through the spin channel to one or more magnetoresistive devices, and sets the magnetization states of the one or more magnetoresistive devices.